In New Radio (NR), a beam failure recovery (BFR) procedure is introduced for a user equipment (UE) to indicate a serving gNB of a new synchronization signal block (SSB) or a new channel state information reference signal (CSI-RS) when beam failure is detected on the serving SSB(s) and/or CSI-RS(s). The BFR procedure is performed via a beam failure detection procedure that works to count beam failure indications received from the lower sublayer(s) to Medium Access Control (MAC) entity.
Moreover, carrier aggregation (CA) is supported in NR and it is assumed that the Primary Cell (PCell) is deployed in Sub 6 GHz (FR1) which can achieve reliable control information transmission while Secondary Cell (SCell) is deployed in above 6 GHz (FR2) which can achieve high throughput. In order to resolve beam blockage (e.g., beam failure) which happened more often in FR2, the BFR is needed to be supported in both PCell and SCell. But, how to efficiently handle the beam failure detection and beam failure recovery procedures among multiple cells (e.g., both PCell and SCell) within a single MAC entity is a challenge. Especially, if a MAC entity receives a request for initiating a new beam failure recovery procedure while another is already ongoing in the MAC entity, it is up to UE implementation whether to continue with the ongoing procedure or start with the new procedure. Hence, during the beam failure detection performed among multiple cells which associated to a single MAC entity for carrier aggregation, it is possible that multiple random access procedures could be requested by the triggered BFRs among the multiple cells, and additional random access procedure(s) could be triggered while one random access procedure has been triggered and currently ongoing.